This invention relates to a rotation sensor unit that detects rotation of a shaft with a magnetic encoder.
As a rotation sensor unit of this type, a rotation sensor unit comprising a rolling bearing having an outer race, a housing in which the outer race of the rolling bearing is fitted, a shaft supported by the rolling bearing and a magnetic encoder for detecting rotation of the shaft is widely used. The encoder of the magnetic encoder should be a magnet having north and south poles provided alternately in the circumferential direction around the axis of the shaft. The encoder is provided coaxially with the shaft so that it rotates integrally with the shaft. The magnetism detection element of the magnetic encoder is provided so that it axially faces the encoder. The area of each surface of the encoder and the magnetism detection element facing axially with each other is much smaller than the area of the end surface of the shaft, and therefore it is essential to stabilize the rotation center of the encoder for high accuracy of detection.
Japanese Patent Publication 3086563B discloses a conventional rotation sensor unit comprising a shaft formed with a recess in one end surface thereof, and an encoder fitted in the hole so that the encoder is positioned coaxially with the shaft. The shaft is made of a non-magnetic material so that flux from the encoder to the magnetism detection element is not caught by the shaft.